Study On Thetobacco Black Shank(Phytophthora Parasitica Var. Nicotianae Breda De Hean) In Western Hunan

Tobacco black shank(Phytophthora parasitica var. nicotianae Breda de Hean) is a soil-borne disease caused by Phytophthora parasitica var. nicotianae Tucker, and it causes great lose to tobacco production.Due to lack of resistant varieties, closely related with weather factors, and it often occurred together with tobacco bacterial wilt, so it was often difficult to control tobacco black shank.Taking tobacco in XiangXi as study object, the pathogenesis regularity and influence factors of tobacco black shank and the integrated control of the disease were studied in this paper. The results were as follows:Hyphae piece traumatic inoculation method, axillary traumatic inoculation method and mycelium suspension injection inoculation method were compared on its inoculation effect.The results indicated that hyphae piece traumatic inoculation method was the optimum method. Virulence of total14strains was determined.The results demonstrated that disease index of total14strains to the variety Honghua dajinyuan were all between50to80and belong to medium virulence level.The strain YS3from YongShun County had the highest disease index,and the strain BJ1from BaoJing County had the lowest disease index.The disease epidemic curve of tobacco black shank in Western Hunan was an untypical "S"type.This disease occurred in early April and gradually increased with time,a peak was reached in early June and progress of disease tend to smooth and steady afterthat.General survey result of desease incidence in five main tobacco counties indicated that this desease occurred in11towns of the surveyed26. towns,which account for46.2%; occurred in25villages of the surveyed77villages, accounting for32.5%; occurred in198fields of the surveyed475fields, accounting for41.2%. The analysis of hunan meteorological factors in western Hunan influence on tobacco black shank disease epidemics indicate that suitable temperature and humidity weather are appropriate for the occurrence and prevalence of tobacco black shank disease.Indoor resistance detection results indicated that disease index of Honghuadajinyuan was the highest,displaying susceptibility.For other tobacco varieties, disease index of RG11and RG17showed medium resistance.The rest six displayed resistance but no variety with high resistance. Results of field resistance identification were similar to indoor resistance results,while disease index all decreased by certain range.Control effect on tobacco black shank of nine fungicides was compared.The results showed that all nine fungicides were safe to tobacco.When the first survey was conducted seven days after treatment,control effect of metalaxyl was the lowest of72.68%,while control effect of other eight treatments were all above80%,of which fluopicolide. propamocarb got the highest control effect of89.26%. The results also showed that control effect of treatment10days after tobacco transplant was better than treatment after morbidity; Control effect of spraying method was1%to2%better than root irrigation method.